Some wireless communication devices may include a transmitter having a Power Amplifier (PA). Some transmitters utilize an outphasing architecture, based on decomposing an input signal into two constant amplitude signals driving two high-efficiency switching amplifiers. For example, two quarter-wave transmission lines are used for power combining, together with two non-isolated switching amplifiers and a common load. Two constant amplitude signals are extracted, and are used to drive the two switching amplifiers. The load seen by each amplifier depends on the relative phase of the input signals. When the output power is low, the load on each amplifier is high. Accordingly, an outphasing PA may be more efficient than a non-outphasing PA, particularly at a low output power region.
In contrast, some wireless communication devices may include a transmitter having a Doherty PA, for example, a high-efficiency linear PA utilizing two separate amplifiers. The Doherty PA includes two amplifiers, namely, a peak amplifier and a carrier amplifier, working in different classes (for example, class B and class C) to achieve linear behavior. A quadrature hybrid coupler provides input signals to the two amplifiers, while an impedance transformer combines the power generated by the two amplifiers. The impedance transformer, for example, a quarter-wave transmission-line, contributes a phase shift of 90 degrees. Accordingly, a quadrature hybrid is utilized such that the output currents are added in-phase. When the peak amplifier begins to conduct (for example, within the upper 6 dB of power range), the impedance seen by the carrier amplifier starts to decrease, and the PA maintains high efficiency.